RESUMO
The qPlus sensor allows for the simultaneous operation of scanning tunneling microscopy (STM) and atomic force microscopy (AFM). When operating a combined qPlus sensor STM/AFM at large tunneling currents, a hitherto unexplained tunneling current-induced cross coupling can occur, which has already been observed decades ago. Here, we study this phenomenon both theoretically and experimentally; its origin is voltage drops on the order of µV that lead to an excitation or a damping of the oscillation, depending on the sign of the current. Ideally, the voltage drops would be phase-shifted by π/2 with respect to a proper phase angle for driving and would, thus, not be a problem. However, intrinsic RC components in the current wiring lead to a phase shift that does enable drive or damping. Our theoretical model fully describes the experimental findings, and we also propose a way to prevent current-induced excitation or damping.
